It is known that if skin is irradiated with light from a light source including, for example, light-emitting diodes (LEDs), and if the reflected light is detected by a photosensor, the amount of reflected light has a pulsatile characteristic in response to the blood flow. Since the pulses of the reflected light correspond to heart beats, the number of heart beats can be estimated from the pulses. The number of heart beats can also be detected by irradiating skin with light, and detecting transmitted light on the other side of the skin. For example, a side of a finger opposite to the nail side is irradiated with light, and the light is detected on the nail side to detect the number of heart beats. These principles are employed in many biosensors intended for use in health care.
So far, the only way to inspect the performance of such biosensors has been to actually attach a biosensor to the skin of a human being and to measure the signals detected. However, it is impossible to keep constant the state of the blood flow of a human being and the state of the attachment of a biosensor. Therefore, it has been difficult to inspect biosensors under stable conditions.
A method of inspecting a biosensor detecting transmitted light has been proposed, in which pulsatile signals are simulated by mechanically inserting and removing a material having a light-absorbing property similar to that of blood into and from the space between a light source and a light-receiving sensor. However, if pulses having a frequency of 1 Hz are to be simulated in this method, the material simulating blood should be moved at a frequency of 1 Hz. Since applying this method causes mechanical vibrations in the inspection device itself, the light incident on the light-receiving unit of the biosensor also has a noise component of 1 Hz. This may lead to an erroneous inspection result indicating that pulses at a frequency of 1 Hz are detected although the biosensor does not meet the required performance.